Lean automation architectures

Technical advances lead to more efficient automation solutions.

Rich Harwell

11/25/2013

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For decades, machine automation architecture has hardly changed. The basic makeup of control systems involved a programmable logic controller (PLC) with discrete and analog I/O running to the end devices, while an electronic operator interface (OI) provided an interface to set up, operate, and maintain the machine.

Technical advances in processing and communications are yielding new capabilities for machine automation. These communications advances are at both the device and enterprise level and are enabling a streamlined automation architecture (see Figure 1).

1) Device level networking enables direct connections to intelligent end devices on a machine and can remove I/O and wiring from the control cabinet. In addition to simpler construction, direct connection to smart devices improves diagnostics and helps to increase machine up time.

2) Enterprise level networking, with the emergence of industrial Ethernet technologies, enables machines to connect into the manufacturing enterprise. This can provide significant value in monitoring operational efficiency, notification and resolution of machine alarms, and remotely troubleshooting and upgrading the automation programs.

In addition to these operational advantages, these technology advances provide an opportunity to streamline the automation architecture into a simpler form shown in Figure 2 where the logic control, operator interface, device level communications, and enterprise level communications have been integrated into one automation component.

For machine original equipment manufacturers (OEMs), advances in device and enterprise-level communications are enabling the combination of visualization and control, and a new level of connectivity. These changes are making it possible to design and build smarter machinery faster at a lower cost. These advantages can be achieved with:

An integrated development environment that allows faster machine design

While somewhat overshadowed by advances in enterprise networking, device-level networks have continued to progress, enabling more cost-effective connection of even simple devices through a network to the logic control within the system. These advances have taken place both within the control cabinet and outside of it, to expand to the sensors and actuators mounted on the machine. The impact of moving from traditional I/O cards and wiring to simple device-level networking in a control cabinet can be seen in Figures 3 and 4.

Device-level networks yield multiple advantages: reducing time to wire and commission the control panel, removing the I/O cards from the system, and improving operational diagnostic information for more reliable systems.

The move away from I/O to networking for connecting sensors, actuators, and human interface in machine control is a key enabler of a combined automation platform. Once the role of the I/O cards in a system is removed or significantly reduced, the value of having a separate PLC from the electronic operator interface (EOI) is also diminished. The processing power available in today’s microprocessors makes handling the operator interface task and the programmable logic control task manageable from one device. Further, as remote access is increasingly important, the case for a combined HMI-PLC is strengthened, changing the basic control system and enabling a leaner automation approach that combines logic, visualization, and connectivity.

HMI-PLC convergence

The manufacturing community stands to make significant productivity gains with the emergence of industrial Ethernet applied to the factory floor. The expanding capabilities of networks and the smart devices that can interface over it are driving improved diagnostics, faster troubleshooting, and overall improvements in machine reliability. With the information that Ethernet connectivity is enabling, there are more opportunities to reduce the time and costs involved in diagnosing and fixing issues before they cause downtime or delay commissioning. These changes also impact the automation systems on machines, demanding a fresh look at the automation architecture and the role of the PLC and HMI in that system.

To better understand the convergence of HMI-PLC functionality and equipment options, a historical perspective of the PLC and OI technology and development is useful. Traditionally, the PLC was developed to provide control, sequencing, and safety functionality for manufacturing processes, replacing systems that involved numerous devices—multiple control relays, timers and drum sequencers, and closed loop controllers. Largely, the I/O cards used to interface to the sensors, actuators, and simple operator interface devices such as push buttons and pilot lights made up the controller.

The electronic operator interface (EOI) was introduced to complement this simple PLC. By connecting to the PLC through a simple serial network connection, the EOI added the ability to present much richer information to the machine operator, replacing some of the simple push button and pilot lights in the process. This historical relationship between the EOI and PLC is shown in Figure 5.

With industrial Ethernet, the advent of remote access in the automation space means increased automation functionality including: historical data capture and exchange, alarm notification and management, and security administration. These features have been introduced into both the PLC and EOI and tend to overlap today, as vendors of both PLC and EOI equipment have vied to address new requirements for historical information, alarming, and security (see Figure 6).

More is not always better and redundancy in EOI and PLC feature sets has several downsides: the needless duplication of hardware (Ethernet is required on both devices), unnecessary complexity of programming (redundant alarm systems), and increased risks of security holes. Instead of two devices with overlapping functionality, one device with a feature set that covers requirements without duplication means less equipment to buy, program, and configure (see Figure 7).

Streamline architecture

Networking at the device and enterprise level is advancing and supporting new, streamlined automation architecture. Ultimately, this convergence can eliminate entire device levels and enable remote intelligence to reduce training costs, while empowering OEMs to take advantage of the best equipment from a range of suppliers.

Integrated architecture is enabling lean automation—boosting efficiencies and reducing waste—in terms of equipment and time. In a highly competitive business environment, providing best-in-class solutions that are intelligent, intuitive, and elegant delivers a real business advantage and yields control systems that are faster to design, commission, and maintain.

The article is focused on PLC used in factory automation on machines, but I recognize the first part of the article on sensor and actuator networking for lean architecture also happening for DCS in the process control industries; digital networking from the very “first meter” at the sensors and actuator taking the place of 4-20 mA and on/off signals. I guess digitization of automation is and industry-wide trend. Just like we see everything else in our daily lives going digital all the way to “end devices” like digital phones, digital cameras, digital TV sets, and digital music players etc. It makes sense for transmitters, actuators, and valve positioners etc. to also go digital.

The “H1” fieldbus technologies used at the sensor/actuator level (i.e. level 1 of the Purdue reference model) in process control are FOUNDATION fieldbus H1 and PROFIBUS-PA etc. For wireless sensors and actuators it is primarily WirelessHART.

Bus technologies have been around for a while but were not as easy to use as they could have been. But I agree technology advancements are now yielding new capabilities. For instance, the Fieldbus Foundation’s usability initiative has made FOUNDATION fieldbus H1 very much easier to use by enhancing the EDDL technology (www.eddl.org) making configuration/setup, calibration, and diagnostics/troubleshooting of fieldbus devices very much easier than in the past. Another important enhancement is backwards compatibility with old DD files so devices can be replaced by a newer version without having to touch the system software. This again makes fieldbus as easy, if not easier, to run and maintain than 4-20 mA and on/off signals. That is, with these enhancements you get the hardware and installation savings of fieldbus, intelligence and diagnostics of fieldbus, but with the ease of use of 4-20 mA and on/off.

I personally agree direct connection of even the lowest level devices like sensors and actuator to networking in order to remove traditional hardwired I/O makes sense and that this results in simple construction. I also agree direct connection of smart devices to networking gives access to diagnostics which can be used to increase plant uptime.

I also agree that Ethernet is for the enterprise level networking at level 3 and 4 of the Purdue reference model. Industrial Ethernet such as Modbus/TCP, PROFINET, and EtherNet/IP are ideal for peripherals like motor drives, motor starters, and MCC at level 1-1/2 of the Purdue model. Industrial Ethernet is making inroads to the domain of “H2” fieldbus such as Modbus/RTU, PROFIBUS-DP, and DeviceNet. These “H2” fieldbuses for level 1-1/2 should not be confused with the “H1” fieldbuses mentioned earlier for level 1.

Used together, “H1” fieldbus and Ethernet enable remote centralized diagnostics and other administration of sensors, transmitters, positioners, actuators, and valves. It is just like USB and Ethernet complementing each other on your laptop.

So yes, automation components at level 2 of the Purdue model straddle the interface between “H1” fieldbuses (level 1) plus industrial Ethernets (level 1-1/2) at the lower levels, and Ethernet (at level 2 and above) at the higher levels.

Indeed the higher level Ethernet networking gets more attention than sensor level bus technologies these days. Yet networking at the sensor and actuator level is crucial to streamlining automation. These “H1” fieldbuses have progressed significantly over the last few years; both the technology itself, but also in better product implementations. The latest enhancements and developments have greatly benefitted fieldbus usability such as EDDL and backwards compatibility simplifying setup/configuration, calibration, diagnostics/troubleshooting, and device replacement.

Inside the control cabinet we see fieldbus power supplies integrated into the interface cards, eliminating the need for separate fieldbus power supplies and associated marshalling cabinets. By eliminating the marshalling cabinets, system footprint is dramatically reduced.

This makes the move from traditional I/O cards and wiring to networking at the lowest level even more attractive.

Anonymous , 11/28/13 10:08 AM:

Continued from previous post...

I agree there are multiple advantages of fieldbus. The time reduction for wiring and commissioning is particularly great when you consider that each device has not signal but many. For instance, a control valve positioner has 2 or 3 signals, an on/off valve has 3 signals, and electric actuator / motor operated valve (MOV) has anywhere from 6-12 signals and so on. Many transmitters and analyzers have 2-3 signals. On average there may be 3 signals per field instrument; meaning an H1 fieldbus eliminates 3 pairs of wires, 3 I/O channels, and 3 barriers per device. That is, a 24,000 I/O system becomes a simple 8,000 fieldbus device system. The reduction in I/O cards, canling, and installation like laying cable, cutting, stripping, labeling, crimping, and screwing is significant.

The better diagnostics from fieldbus devices benefits the run & maintain organization; helping them improve plant uptime. Diagnostics not only gives an early warning of device failure so operations can tend the process. Diagnostics also tells the maintenance team when a device does NOT need maintenance and calibration – operations may suspect the device has a problem, but maintenance can confirm if it does or doesn’t. By not having to pull a valve or a flowmeter for inspection, saves tremendous amount of time. Valves and flowmeters can spend more “time on pipe” instead of in the workshop.

Remember, H1 fieldbus is taking the place of not only 4-20 mA but of on/off signals too. That is, fieldbus does away with most AI and AO cards, but also DI and DO cards.

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